Added CONTRIBUTING.md

[DarikshaAnsari]

Fixes issue #749 :

Description:

The current in-toto repository has no contributing file, and the only information documented is available here, making it challenging for new contributors to get started. This issue aims to add a new contributing file to provide comprehensive and user-friendly instructions for potential contributors.

Proposed Changes:

• Quick Start Guide: Add basic steps for contributing.
• Installation Instructions: Provide detailed setup instructions.
• Contribution Guidelines: Expand on coding standards, testing requirements, and PR process.
• DCO Signing: Explain the importance and provide signing instructions.
• Testing Instructions: Include tox usage and manual testing guidelines.
• Code Formatting: Add guidelines for consistent code formatting.
• Documentation Building: Provide instructions for local documentation generation.

[DarikshaAnsari]

@lukpueh I have change the file location. PTAL!

[lukpueh]

This is great! Many thanks!! I only have a few minor comments:

• I think we should make the headings less prominent to put more emphasis on the contents (see inline code suggestions).
• Links to venv and git --sign-off docs are probably helpful (see inline code suggestions).
• The manual test snippet probably does not work. Please fix (see inline comment).
• Would you mind adding a link to this page in https://github.com/in-toto/in-toto?tab=readme-ov-file#governance-and-contributing?

[lukpueh]

Would you mind adding a link to this page in https://github.com/in-toto/in-toto?tab=readme-ov-file#governance-and-contributing?

Apart from the link this looks great!

[DarikshaAnsari]

I have added link here in contribution guidelines,

[lukpueh]

Ah, okay, I was suggesting to add a link, which points to docs/CONTRIBUTING.md, here:

in-toto/README.md

Lines 153 to 156 in 659942b

	## Governance and Contributing
	For information about in-toto's governance and contributing guidelines, see
	[GOVERNANCE.md](GOVERNANCE.md).

E.g.

 For information about in-toto's governance and contributing guidelines, see 
 [GOVERNANCE.md](GOVERNANCE.md) and [CONTRIBUTING.md](doc/CONTRIBUTING).md.

[lukpueh]

Ah, okay, I was suggesting to add a link, which points to docs/CONTRIBUTING.md, here:

in-toto/README.md

Lines 153 to 156 in 659942b

	## Governance and Contributing
	For information about in-toto's governance and contributing guidelines, see
	[GOVERNANCE.md](GOVERNANCE.md).

E.g.

 For information about in-toto's governance and contributing guidelines, see 
 [GOVERNANCE.md](GOVERNANCE.md) and [CONTRIBUTING.md](doc/CONTRIBUTING).md.

There still seems to be a misunderstanding. I was asking to make the suggested change in REAMDE.md. If you click on the link above, you'll get directly to the section, which I wanted you to update

[lukpueh]

Suggested change

	For information about in-toto's governance and contributing guidelines, see
	[GOVERNANCE.md](GOVERNANCE.md) and [CONTRIBUTING.md](doc/CONTRIBUTING).
	For information about in-toto's governance and contributing guidelines, see
	[GOVERNANCE.md](GOVERNANCE.md) and [CONTRIBUTING.md](doc/CONTRIBUTING.md).

[lukpueh]

Thanks!